1. Field of the Invention
The present invention relates to a control system for controlling a hybrid vehicle having an internal combustion engine and an electric motor as separate propulsion sources, and more particularly to a control system for controlling a hybrid vehicle in regenerating electric energy with an electric motor.
2. Description of the Related Art
There have heretofore been known hybrid vehicles each having an internal combustion engine and an electric motor as separate propulsion sources. There has also been proposed a control system for controlling a hybrid vehicle to increase the regenerative efficiency of an electric motor when it operates in a regenerative mode at the time the hybrid vehicle is decelerating. For example, a control system disclosed in Japanese laid-open patent publication No. 8-112190 fully opens an electrically controlled throttle valve when the electric motor operates in the regenerative mode at the time the hybrid vehicle is decelerating. Accordingly, a mechanical energy loss produced due to pumping losses of the engine when the throttle valve remains closed is reduced, and the kinetic energy of the hybrid vehicle can efficiently be recovered as regenerated energy.
Japanese laid-open patent publication No. 9-135502 discloses a control system for controlling a hybrid vehicle to reduce braking torques applied by engine braking depending on the magnitude of a regenerative braking torque produced by an electric motor when the electric motor operates in a regenerative mode.
The disclosed control system calculates braking torques applied by engine braking when a throttle valve is fully closed and opened, corresponding to the rotational speed of a drive axle at the time the fuel of supply to the engine is stopped while the hybrid vehicle is decelerating. Then, the control system adjusts the regenerative braking torque produced by the electric motor to the range of the calculated braking torques, and operates a throttle valve in an intake passage of the engine in an opening direction depending on the magnitude of the regenerative braking torque produced by the electric motor for thereby reducing the braking torque applied by engine braking. In this manner, an uncomfortable feeling that the driver of the hybrid vehicle has due to a deceleration variation while the hybrid vehicle is running with engine braking applied, and kinetic energy of the hybrid vehicle which has been wasted is recovered as electric energy for better regenerative efficiency.
With the above conventional control system, however, the amount of regenerated energy is limited to the range of the difference between the braking torques produced when the throttle valve is fully closed and opened, and intake air excessively cools the catalytic converter in an exhaust system of the engine because the throttle valve is fully opened while the electric motor is operating in the regenerative mode, with the result that emission characteristics will become impaired when the hybrid vehicle returns from the regenerative mode to an ordinary running mode. Consequently, the control system needs to reduce the regenerative torque generated by the electric motor and to close the throttle valve or to fully close the throttle valve to interrupt the regenerative mode of the electric motor, when the detected temperature of the catalytic converter reaches a predetermined value.
It is therefore an object of the present invention to provide a control system for controlling a hybrid vehicle having an internal combustion engine and an electric motor which can operate in a regenerative mode, to determine a regenerative quantity for the electric motor from a regenerative quantity established based on the decelerating resistance established depending on the vehicle speed when the hybrid vehicle is decelerated and a regenerative quantity established based on the remaining capacity of an electric energy storage unit or the temperature of a drive control circuit for the electric motor, in order to expand a decelerating range for regenerating operation of the electric motor, and to control a pumping loss control unit for the engine based on the determined regenerative quantity.
Another object of the present invention is to provide a control system for controlling a hybrid vehicle to control a pumping loss control unit capable of preventing a catalytic converter from being excessively cooled, depending on a determined regenerative quantity.
Still another object of the present invention is to provide a control system for controlling a hybrid vehicle, which has a pumping loss control unit for controlling pumping losses of the engine of the hybrid vehicle, the pumping loss control unit comprising an exhaust gas recirculation control unit.
Yet still another object of the present invention is to provide a control system for controlling a hybrid vehicle, which has a pumping loss control unit for controlling pumping losses of the engine of the hybrid vehicle, the pumping loss control unit comprising an intake and exhaust valve control unit.
To achieve the above objects, there is provided in accordance with the present invention a control system for controlling a hybrid vehicle having an engine for rotating a drive axle, an electric motor for assisting the engine in rotating the drive axle and converting kinetic energy of the drive axle into electric energy in a regenerative mode, and electric energy storage means connected through a drive control circuit to the electric motor, for storing electric energy, comprising regenerative quantity determining means including first regenerative quantity establishing means for establishing a first regenerative quantity for the electric motor based on a vehicle speed of the hybrid vehicle when the supply of fuel to the engine is stopped upon deceleration of the hybrid vehicle, second regenerative quantity establishing means for establishing a second regenerative quantity for the electric motor based on a remaining capacity of the electric energy storage means, and third regenerative quantity establishing means for establishing a third regenerative quantity for the electric motor based on a temperature of the drive control circuit, and pumping loss controlling means for controlling pumping losses of the engine based on the first, second, and third regenerative quantities established respectively by the first, second, and third regenerative quantity establishing means.
The pumping loss controlling means comprises means for minimizing the pumping losses of the engine if any one of the second and third regenerative quantities established respectively by the second and third regenerative quantity establishing means is at least the first regenerative quantity established by the first regenerative quantity establishing means, and controlling the pumping losses of the engine based on a difference between the first regenerative quantity and the second or third regenerative quantity if any one of the second and third regenerative quantities established respectively by the second and third regenerative quantity establishing means is smaller than the first regenerative quantity established by the first regenerative quantity establishing means.
According to the present invention, there is also provided a control system for controlling a hybrid vehicle having an engine for rotating a drive axle, an electric motor for assisting the engine in rotating the drive axle and converting kinetic energy of the drive axle into electric energy in a regenerative mode, and electric energy storage means connected through a drive control circuit to the electric motor, for storing electric energy, comprising an energy distribution control unit for determining a drive power to be generated by the electric motor based on a drive power of the hybrid vehicle, a vehicle speed of the hybrid vehicle, a remaining capacity of the electric energy storage means, and a running resistance to the hybrid vehicle, regenerative quantity determining means for determining a regenerative quantity based on the vehicle speed, a decelerating resistance, the running resistance, and the remaining capacity of the electric energy storage means, and pumping loss control means for controlling pumping losses of the engine based on the regenerative quantity determined by the regenerative quantity determining means.
In order to prevent a catalytic converter disposed in an exhaust pipe from being excessively cooled, the pumping loss controlling means has an exhaust gas recirculation control valve for controlling an amount of exhaust gases recirculated from the exhaust pipe of the engine to an intake pipe thereof. The exhaust gas recirculation control valve can be opened to reduce pumping losses of the engine, and can be closed to increase pumping losses of the engine.
The pumping loss controlling means has an intake valve or an exhaust valve of the engine and an actuator for fully opening the intake valve or the exhaust valve. The actuator operates to keep at least one of the intake valve and the exhaust valve open thereby to reduce pumping losses of the engine, and to close the intake valve or the exhaust valve which has been kept open thereby to increase pumping losses of the engine.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.